1. Field of the Invention
The present invention relates to a solid-state imaging device incorporated in an imaging apparatus such as a digital camera. More particularly, the invention relates to a photoelectric conversion film-stacked solid-state imaging device that is configured so as to be suitable for use in an imaging apparatus, as well as its manufacturing method.
2. Description of the Related Art
Solid-state imaging devices have a soft surface because its photodetecting surface is provided with microlenses (top lenses) made of resin or the like and a color filter layer. Therefore, it is necessary to protect the photodetecting surface to prevent formation of scratches and sticking of dust etc. To this end, conventionally, a transparent substrate such as a glass substrate is bonded to the photodetecting surface with adhesive (refer to JP-A-2003-31782 and JP-A-2008-92417).
However, there are some problems relating to the material of the adhesive. In conventional solid-state imaging devices such as CCD image sensors and CMOS image sensors, to increase the efficiency of utilization of incident light, microlenses are disposed over respective photodetecting elements. If adhesive having approximately the same refractive index as the microlenses were applied to the surfaces of the microlenses, no light refraction would occur at the surfaces of the microlenses and the function of the microlenses would be impaired, that is, the microlenses could not condense incident light.
For the above reason, the transparent resin as a material of the adhesive should have a smaller refractive index than the microlenses. Furthermore, the reliability of the adhesive is low unless it is made of a material having a small water absorption coefficient. Required to be small in refractive index and water absorption coefficient, the material of the adhesive needs to be selected from only a small number of options, resulting in a problem of cost increase.
JP-B-4271909 discloses a technique that the entire surfaces of microlenses are not bonded to a transparent substrate with adhesive; instead, gaps are formed between the microlenses and the transparent substrate and the light condensing efficiency of the microlenses is increased utilizing the refractive index of air. However, a manufacturing step of forming gaps is complex and hence is a factor of manufacturing cost increase. There is another problem that the gaps make it difficult to reduce the thickness of the solid-state imaging device.